Distribution of the T2-MITE Family Transposons in the Xenopus (Silurana) tropicalis Genome

The T2 family of miniature inverted-repeat transposable elements (T2-MITE) is a prevalent MITE family found in both Xenopus(Silurana) tropicalis and X. laevis. Some subfamilies, particularly T2-A1 and T2-C, may have originated prior to the diversification of the 2 Xenopus lineages and currently include active members in X. tropicalis, whereas another subfamily, T2-E, may have lost its transposition activity even earlier. The distribution of each T2-MITE subfamily in X. tropicalis was investigated and compared to evaluate the evolutionary dynamics of the T2-MITE subfamilies. The subfamilies showed differences in chromosomal distribution, uniformity of insertion density on scaffolds, ratios of upstream to downstream insertions with respect to genes, and their distance from genes. Among these, the T2-C subfamily was interesting because it was frequently inserted upstream and close to genes and because genes with close insertions of this subfamily showed high correlations in spatial expression patterns. This unique distribution and long-lived transposition activity may reflect a mutual relationship evolved between this subfamily and the host.